Organic electroluminescent element, organic electroluminescent unit, and electronic apparatus

ABSTRACT

An organic electroluminescent element includes, in order, a first electrode, an organic light-emitting layer, a metal thin film including a metal or a metal alloy, an organic electron transport layer doped with a metal, and a second electrode. The metal in the metal thin film is identical to the metal doped in the organic electron transport layer. The metal alloy in the metal thin film includes a metal identical to the metal doped in the organic electron transport layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Priority PatentApplication Nos. 2017-122262 filed on Jun. 22, 2017, and 2018-016264filed on Feb. 1, 2018, the entire contents each of which areincorporated herein by reference.

BACKGROUND

The disclosure relates to an organic electroluminescent element, anorganic electroluminescent unit, and an electronic apparatus.

A variety of organic electroluminescent units, such as organicelectroluminescent displays, including organic electroluminescentelements have been proposed. The organic electroluminescent elementseach generate excitons through recombination, in a light-emitting layer,of electrons injected from a cathode and holes injected from an anodeand emit light when the excitons return to a low energy level or aground state. Accordingly, efficient carrier injection is needed for theorganic electroluminescent elements.

Electron injection, which is one of techniques for carrier injection,uses an electron injection layer as an organic layer through whichelectrons are injected into a light-emitting layer. The electroninjection layer includes an organic material doped with a low-workfunction metal. Reference is made to Japanese Unexamined PatentApplication Publication (JP-A) Nos. 2008-98475, 2006-173230, 2007-88015,2013-38432, 2013-102006, 2014-82524, 2015-109470, and 2008-6459, forexample.

SUMMARY

Unfortunately, the use of such an electron injection layer may causediffusion, into the light-emitting layer, of the metal doped in theelectron injection layer. This may possibly lead to a reduction in lightemission efficiency.

It is desirable to provide an organic electroluminescent element, anorganic electroluminescent unit, and an electronic apparatus that makeit possible to suppress a reduction in light emission efficiency.

An organic electroluminescent element according to one embodiment of thedisclosure includes, in order, a first electrode, an organiclight-emitting layer, a metal thin film including a metal or a metalalloy, an organic electron transport layer doped with a metal, and asecond electrode. The metal in the metal thin film is identical to themetal doped in the organic electron transport layer. The metal alloy inthe metal thin film includes a metal identical to the metal doped in theorganic electron transport layer.

An organic electroluminescent element according to one embodiment of thedisclosure includes, in order, a first electrode, an organiclight-emitting layer, a metal thin film including a metal or a metalalloy, an organic electron injection layer doped with a metal, and asecond electrode. The metal in the metal thin film is identical to themetal doped in the organic electron injection layer. The metal alloy inthe metal thin film includes a metal identical to the metal doped in theorganic electron injection layer.

An organic electroluminescent unit according to one embodiment of thedisclosure is provided with a light-emitting panel and a drivingcircuit. The light-emitting panel includes a plurality of organicelectroluminescent elements. The driving circuit is configured to driveeach of the plurality of organic electroluminescent elements. At leastone of the plurality of organic electroluminescent elements includes, inorder, a first electrode, an organic light-emitting layer, a metal thinfilm including a metal or a metal alloy, an organic electron transportlayer doped with a metal, and a second electrode. The metal in the metalthin film is identical to the metal doped in the organic electrontransport layer. The metal alloy in the metal thin film includes a metalidentical to the metal doped in the organic electron transport layer.

An organic electroluminescent unit according to one embodiment of thedisclosure is provided with a light-emitting panel and a drivingcircuit. The light-emitting panel includes a plurality of organicelectroluminescent elements. The driving circuit is configured to driveeach of the plurality of organic electroluminescent elements. At leastone of the plurality of organic electroluminescent elements includes, inorder, a first electrode, an organic light-emitting layer, a metal thinfilm including a metal or a metal alloy, an organic electron injectionlayer doped with a metal, and a second electrode. The metal in the metalthin film is identical to the metal doped in the organic electroninjection layer. The metal alloy in the metal thin film includes a metalidentical to the metal doped in the organic electron injection layer.

An electronic apparatus according to one embodiment of the disclosure isprovided with an organic electroluminescent unit. The organicelectroluminescent unit is provided with a light-emitting panel and adriving circuit. The light-emitting panel includes a plurality oforganic electroluminescent elements. The driving circuit is configuredto drive each of the plurality of organic electroluminescent elements.At least one of the plurality of organic electroluminescent elementsincludes, in order, a first electrode, an organic light-emitting layer,a metal thin film including a metal or a metal alloy, an organicelectron transport layer doped with a metal, and a second electrode. Themetal in the metal thin film is identical to the metal doped in theorganic electron transport layer. The metal alloy in the metal thin filmincludes a metal identical to the metal doped in the organic electrontransport layer.

An electronic apparatus according to one embodiment of the disclosure isprovided with an organic electroluminescent unit. The organicelectroluminescent unit is provided with a light-emitting panel and adriving circuit. The light-emitting panel includes a plurality oforganic electroluminescent elements. The driving circuit is configuredto drive each of the plurality of organic electroluminescent elements.At least one of the plurality of organic electroluminescent elementsincludes, in order, a first electrode, an organic light-emitting layer,a metal thin film including a metal or a metal alloy, an organicelectron injection layer doped with a metal, and a second electrode. Themetal in the metal thin film is identical to the metal doped in theorganic electron injection layer. The metal alloy in the metal thin filmincludes a metal identical to the metal doped in the organic electroninjection layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the disclosure and are incorporated in and constitute apart of this specification. The drawings illustrate example embodimentsand, together with the specification, serve to explain the principles ofthe disclosure.

FIG. 1 illustrates an exemplary cross-sectional configuration of anorganic electroluminescent element according to one embodiment of thedisclosure.

FIG. 2 illustrates a modification example of the cross-sectionalconfiguration of the organic electroluminescent element illustrated inFIG. 1.

FIG. 3 schematically illustrates exemplary energy levels of respectivelayers of the organic electroluminescent element illustrated in FIG. 2.

FIG. 4 schematically illustrates a modification example of the energylevels of the respective layers of the organic electroluminescentelement illustrated in FIG. 2.

FIG. 5 illustrates a modification example of the cross-sectionalconfiguration of the organic electroluminescent element illustrated inFIG. 1.

FIG. 6 illustrates a modification example of the cross-sectionalconfiguration of the organic electroluminescent element illustrated inFIG. 1.

FIG. 7 illustrates an exemplary outline configuration of an organicelectroluminescent unit according to one embodiment of the disclosure.

FIG. 8 illustrates an exemplary circuit configuration of a pixelillustrated in FIG. 7.

FIG. 9 is a perspective view of an external appearance of an electronicapparatus provided with an organic electroluminescent unit according toone embodiment of the disclosure.

FIG. 10 is a perspective view of an external appearance of anillumination apparatus provided with an organic electroluminescentelement according to one embodiment of the disclosure.

DETAILED DESCRIPTION

In the following, some example embodiments of the disclosure aredescribed in detail, in the following order, with reference to theaccompanying drawings. Note that the following description is directedto illustrative examples of the disclosure and not to be construed aslimiting to the disclosure. Factors including, without limitation,numerical values, shapes, materials, components, positions of thecomponents, and how the components are coupled to each other areillustrative only and not to be construed as limiting to the disclosure.Further, elements in the following example embodiments which are notrecited in a most-generic independent claim of the disclosure areoptional and may be provided on an as-needed basis. The drawings areschematic and are not intended to be drawn to scale. Note that the likeelements are denoted with the same reference numerals, and any redundantdescription thereof will not be described in detail. Note that thedescription is given in the following order.

1. First Embodiment (Organic Electroluminescent Element)

2. Modification Example of First Embodiment (Organic ElectroluminescentElement)

3. Second Embodiment (Organic Electroluminescent Unit)

4. Application Examples (Electronic Apparatus and IlluminationApparatus)

1. FIRST EMBODIMENT

[Configuration]

FIG. 1 illustrates an exemplary cross-sectional configuration of anorganic electroluminescent element 1 according to a first embodiment ofthe disclosure. The organic electroluminescent element 1 may be on asubstrate 10, for example. The organic electroluminescent element 1includes an anode 11, a light-emitting layer 14, and a cathode 18, forexample. The light-emitting layer 14 is disposed between the anode 11and the cathode 18. The organic electroluminescent element 1 furtherincludes, for example, a hole injection layer 12 and a hole transportlayer 13, in this order from the anode 11. The hole injection layer 12and the hole transport layer 13 are disposed between the anode 11 andthe light-emitting layer 14. One of the hole injection layer 12 or thehole transport layer 13 may be omitted. The organic electroluminescentelement 1 further includes, for example, an electron transport layer 16and an electron injection layer 17, in this order from thelight-emitting layer 14. The electron transport layer 16 and theelectron injection layer 17 are disposed between the light-emittinglayer 14 and the cathode 18. One of the electron transport layer 16 orthe electron injection layer 17 may be omitted. The organicelectroluminescent element 1 further includes, for example, a diffusionbarrier layer 15 between the light-emitting layer 14 and the electrontransport layer 16. The diffusion barrier layer 15 may include noorganic material. The organic electroluminescent element 1 has astructure that includes, for example, the anode 11, the hole injectionlayer 12, the hole transport layer 13, the light-emitting layer 14, thediffusion barrier layer 15, the electron transport layer 16, theelectron injection layer 17, and the cathode 18, in this order from thesubstrate 10. Optionally, the organic electroluminescent element 1 mayfurther include other functional layers.

The substrate 10 may be, for example, a light-transmissive translucentsubstrate such as a transparent substrate. The substrate 10 may be, forexample but not limited to, a glass substrate including a glassmaterial. In another embodiment, the substrate 10 may be a translucentresin substrate including a translucent resin material, such aspolycarbonate resin or acrylic resin. In still another embodiment, thesubstrate 10 may be a thin-film transistor (TFT) substrate that is to bea backplane of an organic electroluminescent (EL) display unit.

The anode 11 may be on the substrate 10, for example. The anode 11 maybe, for example but not limited to, a transparent electrode havingtranslucency. In an exemplary embodiment, the anode 11 may be atransparent electrically-conductive film including a transparentelectrically-conductive material, such as indium tin oxide (ITO) orindium zinc oxide (IZO). In another exemplary embodiment, the anode 11may be an electrode including aluminum (Al), silver (Ag), an aluminumalloy, or a silver alloy. In still another exemplary embodiment, theanode 11 may be a reflective electrode having light reflectivity. Instill another exemplary embodiment, the anode 11 may be a laminate ofthe reflective electrode and the transparent electrode.

The hole injection layer 12 may inject, to the hole transport layer 13and the light-emitting layer 14, holes injected from the anode 11. Thehole injection layer 12 may include, for example, a material(hereinafter referred to as hole injecting material) that facilitatesthe injection of the holes from the anode 11 into the hole transportlayer 13 and the light-emitting layer 14. Non-limiting examples of thehole injecting material may include oxides of silver (Ag), molybdenum(Mo), chromium (Cr), vanadium (V), tungsten (W), nickel (Ni), andiridium (Ir), and electrically-conductive polymeric materials, such as amixture of polythiophene and polystyrene sulfonate (PEDOT).

The hole transport layer 13 may transport, to the light-emitting layer14, holes injected from the anode 11. The hole transport layer 13 mayinclude, for example, a material (hereinafter referred to as holetransporting material) that transports, to the light-emitting layer 14,holes injected from the anode 11. Non-limiting examples of the holetransporting material may include an arylamine derivative, a triazolederivative, an oxadiazole derivative, an imidazole derivative, apolyarylalkane derivative, a pyrazoline derivative, a pyrazolonederivative, a phenylenediamine derivative, an amino-substituted chalconederivative, an oxazole derivative, a styrylanthracene derivative, afluorenone derivative, a hydrazone derivative, a stilbene derivative, abutadiene compound, a polystyrene derivative, a triphenylmethanederivative, a tetraphenylbenzene derivative, and a combination thereof.

The light-emitting layer 14 may emit fluorescent light in apredetermined color through recombination of holes and electrons. Forexample, the light-emitting layer 14 may be a coated film that is coatedwith a solution by application and drying of the solution. The solutionmay contain an organic light-emitting material as a solute, and asolvent. In another embodiment, the light-emitting layer 14 may be adeposited film.

The light-emitting layer 14 may emit light through generation ofexcitons caused by recombination, in the light-emitting layer 14, ofholes injected from the anode 11 and electrons injected from the cathode18. The light-emitting layer 14 may include an organic light-emittingmaterial, for example. The raw material of the light-emitting layer 14or the organic light-emitting material may be, for example but notlimited to, a combination of a host material and a fluorescent dopantmaterial. In other words, the light-emitting layer 14 may include, asthe organic light-emitting material, the host material and thefluorescent dopant material, for example. The host material may mainlyserve to transport charges such as electrons and holes, and thefluorescent dopant material may serve to emit fluorescent light. Inanother embodiment, the organic light-emitting material may be acombination of two or more host materials and two or more fluorescentdopant materials.

Non-limiting examples of the host material of the light-emitting layer14 may include an amine compound, a condensed polycyclic aromaticcompound, and a heterocyclic compound. Non-limiting examples of theamine compound may include a monoamine derivative, a diamine derivative,a triamine derivative, and a tetraamine derivative. Non-limitingexamples of the condensed polycyclic aromatic compound may include ananthracene derivative, a naphthalene derivative, a naphthacenederivative, a phenanthrene derivative, a chrysene derivative, afluoranthene derivative, a triphenylene derivative, a pentacenederivative, and a perylene derivative. Non-limiting examples of theheterocyclic compound may include a carbazole derivative, a furanderivative, a pyridine derivative, a pyrimidine derivative, a triazinederivative, an imidazole derivative, a pyrazole derivative, a triazolederivative, an oxazole derivative, an oxadiazole derivative, a pyrrolederivative, an indole derivative, an azaindole derivative, anazacarbazole derivative, a pyrazoline derivative, a pyrazolonederivative, and a phthalocyanine derivative.

Non-limiting examples of the fluorescent dopant material of thelight-emitting layer 14 may include a pyrene derivative, a fluoranthenederivative, an arylacetylene derivative, a fluorene derivative, aperylene derivative, an oxadiazole derivative, an anthracene derivative,and a chrysene derivative. In another embodiment, the fluorescent dopantmaterial of the light-emitting layer 14 may be a metal complex. Themetal complex may contain a ligand and atom of metal, such as iridium(Ir), platinum (Pt), osmium (Os), gold (Au), rhenium (Re), or ruthenium(Ru).

The electron transport layer 16 may transport, to the light-emittinglayer 14, electrons injected from the cathode 18. The electron transportlayer 16 may include, for example, a material (hereinafter referred toas electron transporting material) that transport, to the light-emittinglayer 14, electrons injected from the cathode 18. The electron transportlayer 16 may be a deposited film, for example. In one exemplaryembodiment, the electron transport layer 16 may further have acharge-blocking property to suppress tunneling of charges (i.e., holesin the present embodiment) from the light-emitting layer 14 to thecathode 18 and a property to suppress light extinction of thelight-emitting layer 14 in an excitation state.

The electron transporting material may be an aromatic heterocycliccompound containing one or more hetero atoms in a molecule, for example.The aromatic heterocyclic compound may contain, as a skeleton, apyridine ring, a pyrimidine ring, a triazine ring, a benzimidazole ring,a phenanthroline ring, or a quinazoline ring, for example. In anexemplary embodiment, the electron transporting material may be dopedwith a metal having an electron transporting property. The electrontransport layer 16 of the exemplary embodiment may be an organicelectron transport layer doped with the metal. The electron transportlayer 16 including the metal having the electron transporting propertymakes it possible to exhibit an enhanced electron transporting property.Non-limiting examples of the metal doped in the electron transport layer16 may include transition metals, such as ytterbium (Yb).

The electron injection layer 17 may inject, into the electron transportlayer 16 and the light-emitting layer 14, electrons injected from thecathode 18. The electron injection layer 17 may include a material(hereinafter referred to as electron injecting material) thatfacilitates the injection of electrons from the cathode 18 to theelectron transport layer 16 and the light-emitting layer 14. In anexemplary embodiment, the electron injecting material may be an organicmaterial having an electron injecting property and doped with a metalhaving an electron injecting property. The electron injection layer 17of the exemplary embodiment may be an organic electron injection layerdoped with the metal. The metal doped in the electron injection layer 17may be identical to the metal doped in the electron transport layer 16,for example. Non-limiting examples of the metal doped in the electroninjection layer 17 may include transition metals, such as ytterbium(Yb). In the exemplary embodiment, the metal doped in the (organic)electron transport layer 16 may be less in amount than the (organic)electron injection layer 17. This helps to reduce the diffusion of themetal into the light-emitting layer 14 and suppress a reduction in thetransmittance of the electron transport layer 16 and a reduction inlight emission efficiency, compared with a case where the metal doped inthe electron transport layer 16 is the same in amount as the metal dopedin the electron injection layer 17. The amount of the metal doped in the(organic) electron transport layer 16 may be 15 wt %, for example. Inone exemplary embodiment, the amount of the metal doped in the (organic)electron transport layer 16 may be 5 wt % in view of suppressing thediffusion of the metal and a reduction in transmittance. In anotherembodiment, the electron injection layer 17 may be a metal thin filmthat includes a metal identical to the metal doped in the electrontransport layer 16.

Regardless of whether the electron injection layer 17 is the organicelectron injection layer doped with the metal identical to the metaldoped in the electron transport layer 16 or the metal thin filmincluding the metal identical to the metal doped in the electrontransport layer 16, the electron injection layer 17 may be less inthickness than the electron transport layer 16. In an exemplaryembodiment, the electron transport layer 16 may have a thickness greaterthan 15 nm, and the electron injection layer 17 may have a thickness of15 nm or less. Note that electron transport layer 16 thicker than theelectron injection layer 17 is less likely to affect a driving voltageof the organic electroluminescent element 1, because the electrontransport layer 16 may be an electrically-conductive layer doped withthe metal.

The cathode 18 may be, for example but not limited to, a reflectiveelectrode having light reflectivity. In an exemplary embodiment, thecathode 18 may be a metal electrode that includes a metal materialhaving light reflectivity. Non-limiting examples of the metal materialof the cathode 18 may include aluminum (Al), magnesium (Mg), silver(Ag), an aluminum-lithium alloy, and a magnesium-silver alloy. Inanother exemplary embodiment, the cathode 18 may be a transparentelectrode, such as an ITO film. In the present embodiment, the substrate10 and the anode 11 may have translucency, and the cathode 18 may havelight reflectivity. In this case, the organic electroluminescent element1 may have a bottom-emission structure that emits light through thesubstrate 10. Conversely, the substrate 10 and the anode 11 may havelight reflectivity, and the cathode 18 may have translucency in thepresent embodiment. In this case, the organic electroluminescent element1 may have a top-emission structure that emits light through the cathode18.

The diffusion barrier layer 15 is described in detail below. Thediffusion barrier layer 15 may suppress diffusion, into thelight-emitting layer 14, of the metal doped in the electron transportlayer 16 or the electron injection layer 17. The diffusion barrier layer15 is disposed between the light-emitting layer 14 and the electrontransport layer 16 or between the light-emitting layer 14 and theelectron injection layer 17. The diffusion barrier layer 15 may be incontact with the electron transport layer 16 in one embodiment where theelectron transport layer 16 is provided. The diffusion barrier layer 15may be in contact with the electron injection layer 17 in one embodimentwhere the electron transport layer 16 is omitted.

In one embodiment, the diffusion barrier layer 15 is a metal thin filmthat includes a metal identical to the metal doped in the electrontransport layer 16 or the electron injection layer 17. The metal may bea transition metal, such as Yb. In another embodiment, the diffusionbarrier layer 15 is a metal thin film that includes a metal alloyincluding a metal identical to the metal doped in the electron transportlayer 16 or the electron injection layer 17. The metal alloy may be atransition metal alloy, such as YbIn. The metal thin film may have athickness in a range from 0.1 nm to 2 nm, for example. A metal filmhaving a thickness greater than 2 nm may possibly reduce thetransmittance of light passing through the diffusion barrier layer 15. Ametal thin film having a thickness less than 0.1 nm may possibly exhibitlower efficiency in suppressing the diffusion, into the light-emittinglayer 14, of the metal doped in the electron transport layer 16 or theelectron injection layer 17.

[Effects]

Described below are some effects of the organic electroluminescentelement 1 of the present embodiment.

A variety of organic electroluminescent units including organicelectroluminescent elements have been proposed. The organicelectroluminescent elements each generate excitons throughrecombination, in a light-emitting layer, of electrons injected from acathode and holes injected from an anode and emit light when theexcitons return to a low energy level or a ground state. Accordingly,efficient carrier injection is needed for the organic electroluminescentelement.

Electron injection, which is one of techniques for carrier injection,uses an electron injection layer as an organic layer through whichelectrons are injected into a light-emitting layer. The electroninjection layer includes an organic material doped with a low-workfunction metal. Unfortunately, the use of such an electron injectionlayer may cause diffusion, into the light-emitting layer, of the metaldoped in the electron injection layer. This may possibly lead to areduction in light emission efficiency. To address such a concern, JP-ANos. 2008-98475, 2006-173230, 2007-88015, 2013-38432, 2013-102006,2014-82524, 2015-109470, and 2008-6459 each describe a diffusion barrierlayer to suppress the diffusion of the metal doped in the electroninjection layer.

The diffusion barrier layers described in JP-A Nos. 2008-98475,2006-173230, 2007-88015, 2013-38432, 2013-102006, 2014-82524, and2015-109470 each include various organic compounds, such as a crownether derivative, or metal salts thereof, such as fluorides.Unfortunately, these diffusion barrier layers lack of stability. Inparticular, a diffusion barrier layer that includes a salt of an organiccompound including an alkali metal or an alkaline-earth metal mayreadily cause the diffusion, into the light-emitting layer, of the metalin the diffusion barrier layer. The diffusion barrier layer described inJP-A No. 2008-6459 includes a crystalline inorganic material such assilicon (Si). Unfortunately, this diffusion barrier layer is inferior inan electron injection property and an electron transporting property.

In contrast, the diffusion barrier layer 15 or the metal thin film thatis disposed between the light-emitting layer 14 and the electrontransport layer 16 or between the light-emitting layer 14 and theelectron injection layer 17 includes a metal or a metal alloy in anyembodiment of the disclosure. The metal in the diffusion barrier layer15 is identical to the metal doped in the electron transport layer 16 orthe electron injection layer 17. The metal alloy in the diffusionbarrier layer 15 includes a metal identical to the metal doped in theelectron transport layer 16 or the electron injection layer 17. Such adiffusion barrier layer 15 suppresses the diffusion, into thelight-emitting layer 14, of the metal doped in the electron transportlayer 16 or the electron injection layer 17. Further, the diffusionbarrier layer 15 includes the metal identical to the metal in a layer incontact with the diffusion barrier layer 15 (i.e., the electrontransport layer 16 or the electron injection layer 17). Such a diffusionbarrier layer 15 hardly generates an electronic barrier between thediffusion barrier layer 15 and the layer in contact with the diffusionbarrier layer 15. Moreover, even if the metal in the layer in contactwith the diffusion barrier layer 15 (i.e., the electron transport layer16 or the electron injection layer 17) is diffused in a large amount ina portion adjacent to the diffusion barrier layer 15, the portionadjacent to the diffusion barrier layer 15 is prevented from beingdefective. Furthermore, the metal in the diffusion barrier layer 15causes substantially no abnormal reaction to the layer in contact withthe diffusion barrier layer 15. Additionally, the diffusion barrierlayer 15 is a significantly thin film having a thickness in a range from0.1 nm to 2 nm, for example. Such a diffusion barrier layer 15 hardlyhinders the electron injection property and hardly reduces thetransmittance of light passing through the diffusion barrier layer 15.This helps to suppress a reduction in light emission efficiency.

Additionally, the diffusion barrier layer 15 or the metal thin film thatis disposed between the light-emitting layer 14 and the electroninjection layer 17 includes a metal or a metal alloy in any embodimentof the disclosure. The metal in the diffusion barrier layer 15 isidentical to the metal in the electron injection layer 17. The metalalloy in the diffusion barrier layer 15 includes a metal identical tothe metal in the electron injection layer 17. Such a diffusion barrierlayer 15 suppresses the diffusion, into the light-emitting layer 14, ofthe metal in the electron injection layer 17. Further, the diffusionbarrier layer 15 is a significantly thin film having a thickness in arange from 0.1 nm to 2 nm, for example. Such a diffusion barrier layer15 hardly hinders the electron injection property and hardly reduces thetransmittance of light passing through the diffusion barrier layer 15.This helps to suppress a reduction in light emission efficiency.

The metal doped in the electron transport layer 16 or the electroninjection layer 17 may be a transition metal, such as Yb, in anyembodiment of the disclosure. This stabilizes the diffusion barrierlayer 15, suppressing the diffusion, into the light-emitting layer 14,of the metal in the diffusion barrier layer 15. Accordingly, it ispossible to suppress a reduction in light emission efficiency.

The electron transport layer 16 is doped with the metal in anyembodiment of the disclosure. Compared with an electron transport layerdoped with no metal, the electron transport layer 16 helps to retain avoltage to be applied to the organic electroluminescent element 1 at alow level. Further, the metal doped in the electron transport layer 16may be less in amount than the (organic) electron injection layer 17.This helps to reduce the diffusion of the metal into the light-emittinglayer 14 and suppress a reduction in the transmittance of the electrontransport layer 16 and a reduction in light emission efficiency,compared with the case where the metal doped in the electron transportlayer 16 is the same in amount as the metal doped in electron injectionlayer 17. Furthermore, the diffusion barrier layer 15 helps toefficiently suppress the diffusion of the metal into the light-emittinglayer 14. This helps to suppress a reduction in light emissionefficiency while retaining the driving voltage at a low level.

The electron injection layer 17 may be less in thickness than theelectron transport layer 16 in any embodiment of the disclosure. Forexample, the electron transport layer 16 may have a thickness greaterthan 15 nm, and the electron injection layer 17 may have a thickness of15 nm or less. The electron transport layer 16 thicker than the electroninjection layer 17 is less likely to affect the driving voltage of theorganic electroluminescent element 1, because the electron transportlayer 16 may be an electrically-conductive layer doped with the metal.Accordingly, it is possible to adjust the organic electroluminescentelement 1 to a high-order cavity mode by increasing the thickness of theelectron transport layer 16. A reduction in light emission efficiency isstill suppressed after the adjustment of the organic electroluminescentelement 1 to a high order cavity mode.

2. MODIFICATION EXAMPLE OF FIRST EMBODIMENT Modification Example A

In the foregoing embodiments, increasing the thickness of the diffusionbarrier layer 15 helps to sufficiently suppress the diffusion of themetal, whereas readily impairing transmittance and light emissionefficiency. Additionally, reducing the thickness of the diffusionbarrier layer 15 may possibly impair the diffusion barrier property ofthe diffusion barrier layer 15, whereas helping to increase thetransmittance of the diffusion barrier layer 15 and the light emissionefficiency. In this way, the transmittance and the light emissionefficiency are in a tradeoff relation. Further, the diffusion barrierlayer 15 may be in direct contact with the light-emitting layer 14 inthe foregoing embodiments. This may possibly cause light extinction andminor diffusion, into the light-emitting layer 14, of the metal in thediffusion barrier layer 15.

To address such concerns, the organic electroluminescent element 1 ofany embodiment of the disclosure may further include a buffer layer 19between the light-emitting layer 14 and the diffusion barrier layer 15,as illustrated in FIG. 2, for example. The buffer layer 19 may includean electrically-conductive organic material. Note that one of the holeinjection layer 12 or the hole transport layer 13 illustrated in FIG. 2may be omitted, and one of the electron transport layer 16 or theelectron injection layer 17 illustrated in FIG. 2 may be omitted. In oneembodiment, the buffer layer 19 may be in contact with thelight-emitting layer 14. In another embodiment, the buffer layer 19 maybe in non-contact with the light-emitting layer 14.

The buffer layer 19 may prevent a direct contact between thelight-emitting layer 14 and the diffusion barrier layer 15. The bufferlayer 19 may be disposed between the light-emitting layer 14 and theelectron transport layer 16 or between the light-emitting layer 14 andthe electron injection layer 17. The buffer layer 19 may be disposedcloser to the light-emitting layer 14 than the diffusion barrier layer15. The buffer layer 19 may also serve as a hole-blocking layer. Thebuffer layer 19 may include, for example, a i-electron system lowmolecular organic material, such as an oxadiazole derivative (OXD), atriazole derivative (TAZ), or a phenanthroline derivative (BCP, Bphen).

FIG. 3 schematically illustrates exemplary energy levels of therespective layers of the organic electroluminescent element 1 of thepresent modification example.

The upper line of each layer including an organic material indicates thelowest unoccupied molecular orbital (LUMO), and the lower line indicatesthe highest occupied molecular orbital (HOMO). In FIG. 3, E1 representsthe work function of the diffusion barrier layer 15, and E2 representsthe LUMO energy level of the buffer layer 19. As illustrated in FIG. 3,E2 may be lower than E1, and E1 and E2 may satisfy the followingexpression.|E1−E2|>0  Expression (1)In one embodiment, E1 and E2 may further satisfy the followingexpression.0<|E1−E2|<0.6 eV  Expression (2)E1 and E2 that are excessively close to each other may cause overlappingof electron orbitals, forming metal complexes in the buffer layer 19.The metal complexes formed in the buffer layer 19 may diffuse into thelight-emitting layer 14, possibly resulting in a reduction in lightemission efficiency. Accordingly, the buffer layer 19 may include anorganic material that forms no metal complex even when the buffer layeris in contact with the diffusion barrier layer 15. Additionally, E1 andE2 that are excessively close to each other may readily cause lightextinction. Conversely, E1 and E2 that are excessively far from eachother may increase the driving voltage of the organic electroluminescentelement 1 to an excessively high level. For example, if the differencebetween E1 and E2 is 0.6 eV or greater, the driving voltage of theorganic electroluminescent element 1 may be several volts. To retain thedriving voltage at around one volt or less, E1 and E2 may satisfy thefollowing expression.0.2<|E1−E2|<0.4 eV  Expression (3)In one embodiment, |E1−E2| may be 0.3 eV.

In the present modification example, the diffusion barrier layer 15 andthe buffer layer 19 may be disposed between the light-emitting layer 14and the electron transport layer 16 or between the light-emitting layer14 and the electron injection layer 17. The diffusion barrier layer 15may be thinner than the buffer layer 19 and the buffer layer 19 may bethicker than the diffusion barrier layer 15. This helps to efficientlysuppress the diffusion of the metal and sufficiently increase thetransmittance of the diffusion barrier layer 15 and the buffer layer 19.In the present modification example, the diffusion barrier layer 15 maybe in non-contact with the light-emitting layer 14, and E1 and E2 maysatisfy Expression (1), and optionally Expressions (2) and (3). Thisreduces occurrence of light extinction and suppresses or prevents thediffusion, into the light-emitting layer 14, of the metal in thediffusion barrier layer 15. Consequently, it is possible to suppress areduction in light emission efficiency while retaining the drivingvoltage at a low level.

In another modification example, E2 may be higher than E1, asillustrated in FIG. 4, and E1 and E2 may satisfy Expression (1)described above.

Modification Example B

The organic electroluminescent element 1 of any embodiment of thedisclosure may further include a film-thickness adjusting layer 22, asillustrated in FIGS. 5 and 6, for example. The film-thickness adjustinglayer 22 may be disposed on one side, adjacent to the light-emittinglayer 14, of the cathode 18. In one embodiment where both of theelectron transport layer 16 and the electron injection layer 17 areprovided in the organic electroluminescent element 1, the film-thicknessadjusting layer 22 may be disposed, for example, between the electroninjection layer 17 and the cathode 18 and may be in contact with theelectron injection layer 17. In one embodiment where the electroninjection layer 17 is omitted and the electron transport layer 16 isprovided, the film-thickness adjusting layer 22 may be disposed, forexample, between the electron transport layer 16 and the cathode 18 andmay be in contact with the electron transport layer 16.

The film-thickness adjusting layer 22 may adjust the distance betweenthe anode 11 and the cathode 18 to a predetermined optical path length.The film-thickness adjusting layer 22 may include, for example, atransparent electrically-conductive material, such as ITO or IZO. Thefilm-thickness adjusting layer 22 may be an ITO layer or an IZO layer,for example. These materials, ITO and IZO, are highly transparent andlow-resistive materials. The ITO or IZO layer used as the film-thicknessadjusting layer 22 may have a thickness greater than 15 nm, for example.

The use of the film-thickness adjusting layer 22 enables an adjustmentof the optical path length to any value. This helps to improve lightextraction efficiency. In general, the ITO or IZO layer may be formed bysputtering. During the sputtering, an underlayer of the ITO or IZO layermay be damaged, causing short-circuiting, leakage, a reduction in lightemission efficiency, an increase in driving voltage, or any otherdegradation in organic electroluminescent characteristics. A possiblesolution to suppress the sputtering damage and the degradation inorganic electroluminescent characteristics is the use of an underlayerincluding, for example, an organic material doped with a low-workfunction metal for the formation of the ITO or IZO layer.

In the present modification example, the electron transport layer 16 orthe electron injection layer 17 may serve as the underlayer of thefilm-thickness adjusting layer 22. In detail, the electron transportlayer 16 or the electron injection layer 17 that includes an organicmaterial doped with a metal and serves as the underlayer of thefilm-thickness adjusting layer 22 helps to improve light extractionefficiency, while suppressing the degradation in organicelectroluminescent characteristics. Additionally, the diffusion barrierlayer 15 is disposed between the light-emitting layer 14 and thefilm-thickness adjusting layer 22. In one embodiment, the electrontransport layer 16 or the electron injection layer 17 may include theorganic material doped with a metal, and the diffusion barrier layer 15is a metal thin film that includes a metal identical to the metal dopedin the electron transport layer 16 or the electron injection layer 17 ora metal alloy including a metal identical to the metal doped in theelectron transport layer 16 or the electron injection layer 17. Such adiffusion barrier layer 15 suppresses the diffusion, into thelight-emitting layer 14, of the metal doped in the electron transportlayer 16 or the electron injection layer 17. This helps to suppress areduction in light emission efficiency due to the damage on theunderlayer (i.e., the electron transport layer 16 or the electroninjection layer 17) of the film-thickness adjusting layer 22. Asdescribed hereinabove, the film-thickness adjusting layer 22 helps toimprove light extraction efficiency, the electron transport layer 16 orthe electron injection layer 17 helps to suppress the degradation inorganic electroluminescent characteristics, and the diffusion barrierlayer 15 helps to suppress a reduction in light emission efficiency, inthe present modification example.

3. SECOND EMBODIMENT

[Configuration]

FIG. 7 illustrates an exemplary outline configuration of an organicelectroluminescent unit 2 according to a second embodiment of thedisclosure. FIG. 8 illustrates an exemplary circuit configuration of apixel 21 in the organic electroluminescent unit 2. The organicelectroluminescent unit 2 includes, for example, a display panel 20, acontroller 30, and a driver 40. The driver 40 may be mounted on an outeredge portion of the display panel 20. The display panel 20 may include aplurality of pixels 21 arranged in matrix. The controller 30 and thedriver 40 may drive the display panel 20 (i.e., the pixels 21) on thebasis of an image signal Din and a synchronizing signal Tin receivedfrom an external device.

[Display Panel 20]

In response to the active-matrix driving of the pixels 21 performed bythe controller 30 and the driver 40, the display panel 20 may display animage based on the image signal Din and the synchronizing signal Tinreceived from the external device. The display panel 20 may include aplurality of scanning lines WSL and a plurality of power lines DSL bothextending in a row direction, a plurality of signal lines DTL extendingin a column direction, and the plurality of pixels 21 arranged inmatrix. The display panel 20 may include a substrate supporting thepixels 21, for example. Non-limiting examples of the substratesupporting the pixels 21 may include a glass substrate and a flexiblesubstrate.

The scanning lines WSL may be used to select the pixels 21. In detail,the scanning lines WSL may supply a selection pulse to the pixels 21 toselect the pixels 21 on a predetermined unit basis. In an exemplaryembodiment, the pixels 21 are selected on a pixel-row basis. The signallines DTL may supply, to the respective pixels 21, a signal voltage Vsigcorresponding to the image signal Din. In detail, the signal lines DTLmay supply, to the respective pixels 21, a data pulse including thesignal voltage Vsig. The power lines DSL may supply electric power tothe pixels 21.

The plurality of pixels 21 may include ones emitting red light, onesemitting green light, and ones emitting blue light, for example. In oneembodiment, the pixels 21 may further include ones emitting light inanother color, such as white or yellow.

The signal lines DTL may be each coupled to an output end of ahorizontal selector 41 described below. Each of the signal lines DTL maybe assigned to a corresponding pixel column, for example. The scanninglines WSL may be each coupled to an output end of a write scanner 42described below. Each of the scanning lines WSL may be assigned to acorresponding pixel row, for example. The power lines DSL may be eachcoupled to an output end of a power source. Each of the power lines DSLmay be assigned to a corresponding pixel row, for example.

The pixels 21 may each include, for example, a pixel circuit 21A and anorganic electroluminescent element 21B. The organic electroluminescentelement 21B may be, for example, the organic electroluminescent element1 of any embodiment of the disclosure. At least one of the pixels 21 inthe display panel 20 may include the organic electroluminescent element1 of any embodiment of the disclosure. In other words, at least one ofthe organic electroluminescent elements 21B in the display panel 20 maybe the organic electroluminescent element 1 of any embodiment of thedisclosure. For example, the pixels 21 emitting blue light may eachinclude, as the organic electroluminescent element 21B, the organicelectroluminescent element 1 of any embodiment of the disclosure.

The pixel circuit 21A may control light emission and light extinction ofthe organic electroluminescent element 21B. The pixel circuit 21A mayhold a voltage written into the corresponding pixel 21 through writescanning described below. The pixel circuit 21A may include a drivingtransistor Tr1, a switching transistor Tr2, and a storage capacitor Cs,for example.

The switching transistor Tr2 may control application of the signalvoltage Vsig to a gate of the driving transistor Tr1. The signal voltageVsig may be based on the image signal Din. In one embodiment, theswitching transistor Tr2 may sample a voltage of the signal line DTL andwrite the sampled voltage into the gate of the driving transistor Tr1.The driving transistor Tr1 may be coupled in series to the organicelectroluminescent element 21B. The driving transistor Tr1 may drive theorganic electroluminescent element 21B. The driving transistor Tr1 maycontrol an electric current flowing through the organicelectroluminescent element 21B on the basis of the magnitude of thevoltage sampled at the switching transistor Tr2. The storage capacitorCs may hold a predetermined voltage between the gate and a source of thedriving transistor Tr1. The storage capacitor Cs may retain agate-source voltage Vgs of the driving transistor Tr1 at a constantlevel for a predetermined period. Note that the pixel circuit 21A mayhave a circuit configuration that includes the 2Tr1C circuit describedabove and additional capacitors and transistors. In another embodiment,the pixel circuit 21A may have a circuit configuration different fromthat of the 2Tr1C circuit described above.

Each of the signal lines DTL may be coupled to an output end of thehorizontal selector 41 described below and a source or a drain of theswitching transistor Tr2. Each of the scanning lines WSL may be coupledto an output end of the write scanner 42 described below and a gate ofthe switching transistor Tr2. Each of the power lines DSL may be coupledto an output end of a power supply circuit 33 and the source or a drainof the driving transistor Tr1.

The gate of the switching transistor Tr2 may be coupled to thecorresponding scanning line WSL. One of the source or the drain of theswitching transistor Tr2 may be coupled to the corresponding signal lineDTL. The other of the source or the drain, which is not coupled to thesignal line DTL, of the switching transistor Tr2 may be coupled to thegate of the driving transistor Tr1. One of the source or the drain ofthe driving transistor Tr1 may be coupled to the corresponding powerline DSL. The other of the source or the drain, which is not coupled tothe power line DSL, of the driving transistor Tr1 may be coupled to theanode 11 of the organic electroluminescent element 21B. One end of thestorage capacitor Cs may be coupled to the gate of the drivingtransistor Tr1. The other end of the storage capacitor Cs may be coupledto one of the source or the drain, adjacent to the organicelectroluminescent element 21B, of the driving transistor Tr1.

[Driver 40]

The driver 40 may include the horizontal selector 41 and the writescanner 42, for example. The horizontal selector 41 may apply the analogsignal voltage Vsig to each of the signal lines DTL, in response to orin synchronization with a control signal, for example. The analog signalvoltage Vsig may be transmitted from the controller 30. The writescanner 42 may scan the pixels 21 on a predetermined unit basis.

[Controller 30]

The controller 30 is described in detail below. The controller 30 mayperform predetermined correction on the digital image signal Din andgenerate the signal voltage Vsig on the basis of the image signalobtained through the predetermined correction, for example. The imagesignal Din may be transmitted from an external device, for example. Thecontroller 30 may output the generated signal voltage Vsig to thehorizontal selector 41, for example. The controller 30 may transmit acontrol signal to each circuit in the driver 40, in response to or insynchronization with the synchronizing signal Tin. The synchronizingsignal may be transmitted from an external device, for example.

[Effects]

In any embodiment of the disclosure, at least one of the organicelectroluminescent elements 21B in the display panel 20 may be theorganic electroluminescent element 1 of any embodiment of thedisclosure. Consequently, the organic electroluminescent unit 2 exhibitshigh light emission efficiency.

4. APPLICATION EXAMPLES Application Example 1

Described below is an application example of the organicelectroluminescent unit 2 of the second embodiment. The organicelectroluminescent unit 2 is applicable to a variety of display units ofelectronic apparatuses that display, as images or pictures, imagesignals received from external devices or generated inside the displayunits. Non-limiting examples of the electronic apparatuses may includetelevisions, digital cameras, notebook personal computers, sheet-likepersonal computers, portable terminal devices such as mobile phones, andvideo cameras.

FIG. 9 is a perspective view of an external appearance of an electronicapparatus 3 of the present application example. The electronic apparatus3 may be, for example, a sheet-like personal computer including a body310 having a display surface 320 on a main face. The organicelectroluminescent unit 2 may be provided on the display surface 320 ofthe electronic apparatus 3. The organic electroluminescent unit 2 may bedisposed such that the display panel 20 faces outward. The electronicapparatus 3 of the present application example including the organicelectroluminescent unit 2 on the display surface 320 exhibits high lightemission efficiency.

Application Example 2

Described below is an application example of the organicelectroluminescent element 1 of the first embodiment. The organicelectroluminescent element 1 is applicable to a variety of light sourcesin illumination apparatuses for table lightings, or floor lightings, androom lightings.

FIG. 10 illustrates an external appearance of an illumination apparatusfor a room lighting to which the organic electroluminescent elements 1are applied. The illumination apparatus may include, for example,illuminating sections 410 each including one or more of the organicelectroluminescent elements 1. An appropriate number of the illuminatingsections 410 are disposed at appropriate intervals on a ceiling 420.Note that the illuminating sections 410 may be installed on any placeother than the ceiling 420, such as a wall 430 or a non-illustratedfloor, depending on the intended use.

The illumination apparatus may perform illumination with light emittedfrom the organic electroluminescent elements 1. Accordingly, theillumination apparatus exhibits high light emission efficiency.

Although the disclosure is described hereinabove with reference to theembodiments, modification examples, and application examples, theseembodiments, modification examples, and application examples are not tobe construed as limiting the scope of the disclosure and may be modifiedin a wide variety of ways. It should be noted that the effects describedhereinabove are mere examples. Effects of one embodiment of thedisclosure are not limited to those described hereinabove. Thedisclosure may further include any effects other than those describedhereinabove.

Moreover, the disclosure may have the following configurations, forexample.

(1) An organic electroluminescent element including, in order:

a first electrode;

an organic light-emitting layer;

a metal thin film including a metal or a metal alloy;

an organic electron transport layer doped with a metal; and

a second electrode,

the metal in the metal thin film being identical to the metal doped inthe organic electron transport layer, the metal alloy in the metal thinfilm including a metal identical to the metal doped in the organicelectron transport layer.

(2) The organic electroluminescent element according to (1), in whichthe metal doped in the organic electron transport layer is a transitionmetal.

(3) The organic electroluminescent element according to (2), in whichthe metal doped in the organic electron transport layer is ytterbium(Yb).

(4) The organic electroluminescent element according to any one of (1)to (3), in which the metal thin film has a thickness in a range from 0.1nm to 2 nm.

(5) The organic electroluminescent element according to any one of (1)to (4), further including a film-thickness adjusting layer that isprovided between the organic electron transport layer and the secondelectrode and includes a transparent electrically-conductive material.(6) The organic electroluminescent element according to any one of (1)to (4), further including an organic electron injection layer that isprovided between the organic electron transport layer and the secondelectrode and doped with a metal identical to the metal doped in theorganic electron transport layer.(7) The organic electroluminescent element according to (6), in whichthe metal doped in the organic electron transport layer is less inamount than the metal doped in the organic electron injection layer.(8) The organic electroluminescent element according to (6) or (7), inwhich the organic electron transport layer has a thickness greater than15 nm.(9) The organic electroluminescent element according to any one of (6)to (8), in which the organic electron injection layer has a thickness of15 nm or less.(10) The organic electroluminescent element according to any one of (1)to (4), further including an electron injection layer that is providedbetween the organic electron transport layer and the second electrodeand includes a metal identical to the metal doped in the organicelectron transport layer.(11) The organic electroluminescent element according to (10), in whichthe organic electron transport layer has a thickness greater than 15 nm.(12) The organic electroluminescent element according to (10) or (11),in which the electron injection layer has a thickness of 15 nm or less.(13) An organic electroluminescent element including, in order:

a first electrode;

an organic light-emitting layer;

a metal thin film including a metal or a metal alloy;

an organic electron injection layer doped with a metal; and

a second electrode,

the metal in the metal thin film being identical to the metal doped inthe organic electron injection layer, the metal alloy in the metal thinfilm including a metal identical to the metal doped in the organicelectron injection layer.

(14) The organic electroluminescent element according to (13), in whichthe metal doped in the organic electron injection layer is a transitionmetal.

(15) The organic electroluminescent element according to (14), in whichthe metal doped in the organic electron injection layer is ytterbium(Yb).

(16) The organic electroluminescent element according to any one of (13)to (15), in which the metal thin film has a thickness in a range from0.1 nm to 2 nm.

(17) The organic electroluminescent element according to any one of (6)to (9) and (13) to (16), further including a film-thickness adjustinglayer that is provided between the organic electron injection layer andthe second electrode and includes a transparent electrically-conductivematerial.(18) The organic electroluminescent element according to any one of (10)to (12), further including a film-thickness adjusting layer that isprovided between the electron injection layer and the second electrodeand includes a transparent electrically-conductive material.(19) An organic electroluminescent unit provided with a light-emittingpanel and a driving circuit, the light-emitting panel including aplurality of organic electroluminescent elements, the driving circuitbeing configured to drive each of the plurality of organicelectroluminescent elements, at least one of the plurality of organicelectroluminescent elements including, in order:

a first electrode;

an organic light-emitting layer;

a metal thin film including a metal or a metal alloy;

an organic electron transport layer doped with a metal; and

a second electrode,

the metal in the metal thin film being identical to the metal doped inthe organic electron transport layer, the metal alloy in the metal thinfilm including a metal identical to the metal doped in the organicelectron transport layer.

(20) An organic electroluminescent unit provided with a light-emittingpanel and a driving circuit, the light-emitting panel including aplurality of organic electroluminescent elements, the driving circuitbeing configured to drive each of the plurality of organicelectroluminescent elements, at least one of the plurality of organicelectroluminescent elements including, in order:

a first electrode;

an organic light-emitting layer;

a metal thin film including a metal or a metal alloy;

an organic electron injection layer doped with a metal; and

a second electrode,

the metal in the metal thin film being identical to the metal doped inthe organic electron injection layer, the metal alloy in the metal thinfilm including a metal identical to the metal doped in the organicelectron injection layer.

(21) An electronic apparatus with an organic electroluminescent unit,the organic electroluminescent unit being provided with a light-emittingpanel and a driving circuit, the light-emitting panel including aplurality of organic electroluminescent elements, the driving circuitbeing configured to drive each of the plurality of organicelectroluminescent elements, at least one of the plurality of organicelectroluminescent elements including, in order:

a first electrode;

an organic light-emitting layer;

a metal thin film including a metal or a metal alloy;

an organic electron transport layer doped with a metal; and

a second electrode,

the metal in the metal thin film being identical to the metal doped inthe organic electron transport layer, the metal alloy in the metal thinfilm including a metal identical to the metal doped in the organicelectron transport layer.

(22) An electronic apparatus with an organic electroluminescent unit,the organic electroluminescent unit being provided with a light-emittingpanel and a driving circuit, the light-emitting panel including aplurality of organic electroluminescent elements, the driving circuitbeing configured to drive each of the plurality of organicelectroluminescent elements, at least one of the plurality of organicelectroluminescent elements including, in order:

a first electrode;

an organic light-emitting layer;

a metal thin film including a metal or a metal alloy;

an organic electron injection layer doped with a metal; and

a second electrode,

the metal in the metal thin film being identical to the metal doped inthe organic electron injection layer, the metal alloy in the metal thinfilm including a metal identical to the metal doped in the organicelectron injection layer.

In the organic electroluminescent element, the organicelectroluminescent unit, and the electronic apparatus according to oneembodiment of the disclosure, the metal thin film is disposed betweenthe organic light-emitting layer and the organic electron transportlayer. The metal thin film includes a metal identical to the metal dopedin the organic electron transport layer or a metal alloy including ametal identical to the metal doped in the organic electron transportlayer. Accordingly, it is possible to suppress a reduction in lightemission efficiency.

In the organic electroluminescent element, the organicelectroluminescent unit, and the electronic apparatus according to oneembodiment of the disclosure, the metal thin film is disposed betweenthe organic light-emitting layer and the organic electron injectionlayer. The metal thin film includes a metal identical to the metal dopedin the organic electron injection layer or a metal alloy including ametal identical to the metal doped in the organic electron injectionlayer. Accordingly, it is possible to suppress a reduction in lightemission efficiency.

It should be noted that the description hereinabove is merelyexemplified. The effects of the disclosure are not limited to thosedescribed hereinabove. The disclosure may include some effects differentfrom those described hereinabove and may further include additionaleffects.

Although the disclosure has been described in terms of exemplaryembodiments, it is not limited thereto. It should be appreciated thatvariations may be made in the described embodiments by persons skilledin the art without departing from the scope of the disclosure as definedby the following claims. The limitations in the claims are to beinterpreted broadly based on the language employed in the claims and notlimited to examples described in this specification or during theprosecution of the application, and the examples are to be construed asnon-exclusive. For example, in this disclosure, the use of the termsfirst, second, etc. do not denote any order or importance, but ratherthe terms first, second, etc. are used to distinguish one element fromanother. Moreover, no element or component in this disclosure isintended to be dedicated to the public regardless of whether the elementor component is explicitly recited in the following claims.

What is claimed is:
 1. An organic electroluminescent element comprising,in order: a first electrode; an organic light-emitting layer; a metalthin film including a metal or a metal alloy; an organic electrontransport layer doped with a metal; and a second electrode, the metal inthe metal thin film being the same as the metal doped in the organicelectron transport layer, the metal alloy in the metal thin filmincluding a metal the same as the metal doped in the organic electrontransport layer.
 2. The organic electroluminescent element according toclaim 1, wherein the metal doped in the organic electron transport layercomprises a transition metal.
 3. The organic electroluminescent elementaccording to claim 2, wherein the metal doped in the organic electrontransport layer comprises ytterbium.
 4. The organic electroluminescentelement according to claim 1, wherein the metal thin film has athickness in a range from 0.1 nm to 2 nm.
 5. The organicelectroluminescent element according to claim 1, further comprising afilm-thickness adjusting layer that is provided between the organicelectron transport layer and the second electrode and includes atransparent electrically-conductive material.
 6. The organicelectroluminescent element according to claim 1, further comprising anorganic electron injection layer that is provided between the organicelectron transport layer and the second electrode and doped with a metalidentical to the same as the metal doped in the organic electrontransport layer.
 7. The organic electroluminescent element according toclaim 6, wherein the metal doped in the organic electron transport layeris less in amount than the metal doped in the organic electron injectionlayer.
 8. The organic electroluminescent element according to claim 6,wherein the organic electron transport layer has a thickness greaterthan 15 nm.
 9. The organic electroluminescent element according to claim6, wherein the organic electron injection layer has a thickness of 15 nmor less.
 10. The organic electroluminescent element according to claim1, further comprising an electron injection layer that is providedbetween the organic electron transport layer and the second electrodeand includes a metal the same as the metal doped in the organic electrontransport layer.
 11. The organic electroluminescent element according toclaim 10, wherein the organic electron transport layer has a thicknessgreater than 15 nm.
 12. The organic electroluminescent element accordingto claim 10, wherein the electron injection layer has a thickness of 15nm or less.
 13. The organic electroluminescent element according toclaim 10, further comprising a film-thickness adjusting layer that isprovided between the electron injection layer and the second electrodeand includes a transparent electrically-conductive material.
 14. Anorganic electroluminescent element comprising, in order: a firstelectrode; an organic light-emitting layer; a metal thin film includinga metal or a metal alloy; an organic electron injection layer doped witha metal; and a second electrode, the metal in the metal thin film beingthe same as the metal doped in the organic electron injection layer, themetal alloy in the metal thin film including a metal the same as themetal doped in the organic electron injection layer.
 15. The organicelectroluminescent element according to claim 14, wherein the metaldoped in the organic electron injection layer comprises a transitionmetal.
 16. The organic electroluminescent element according to claim 15,wherein the metal doped in the organic electron injection layercomprises ytterbium.
 17. The organic electroluminescent elementaccording to claim 14, wherein the metal thin film has a thickness in arange from 0.1 nm to 2 nm.
 18. The organic electroluminescent elementaccording to claim 14, further comprising a film-thickness adjustinglayer that is provided between the organic electron injection layer andthe second electrode and includes a transparent electrically-conductivematerial.
 19. An electronic apparatus with an organic electroluminescentunit, the organic electroluminescent unit being provided with alight-emitting panel and a driving circuit, the light-emitting panelincluding a plurality of organic electroluminescent elements, thedriving circuit being configured to drive each of the plurality oforganic electroluminescent elements, at least one of the plurality oforganic electroluminescent elements comprising, in order: a firstelectrode; an organic light-emitting layer; a metal thin film includinga metal or a metal alloy; an organic electron transport layer doped witha metal; and a second electrode, the metal in the metal thin film beingthe same as the metal doped in the organic electron transport layer, themetal alloy in the metal thin film including a metal the same as themetal doped in the organic electron transport layer.